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#1 2019-08-18 09:47:05

Calliban
Member
From: Northern England, UK
Registered: 2019-08-18
Posts: 603

Colonizing / terraforming small asteroids

Greetings! I am new to the board and have been interested in space travel and space colonisation for as long as I can remember.  I thought as my first post here, I would share an idea that I have been working on.

The idea of building human settlements in pressurised spaces in hollow asteroids is quite an old one and goes back to the work of Dandridge Cole in the 1960s.  The idea has a number of problems, chief amongst them being that asteroids are not rigid structures and unless internal pressure can be counteracted by the force of gravity, the asteroid is likely to fail catastrophically and the air, along with human occupants, would be blown out into space.

Small near Earth asteroids are one of the best options for near term space colonisation, due to their proximity to Earth, their abundance of rare metals, which could be mined and returned to Earth and their low escape velocity.  Burrowing into the asteroid allows miners to protect themselves from micro meteorites, space radiation and thermal extremes.

I want to explore the idea of structurally reinforcing small asteroids with high strength polymers and carbon fibres to allow them to withstand internal pressure.  My base case is a 100m diameter asteroid.  If density is typical of a stony asteroid, it would mass 1.3 million tonnes.  Upon arriving at the asteroid, we would wrap it in a fibre reinforced polymer bag, with airlocks fitted into it.  The bag would then be tightened around the asteroid to provide prestressing.  We would them enter through airlocks and mine out the interior of the asteroid and pressurise the tunnels created.  The tunnels would probably have to be lined with a polyethylene wall paper to prevent air from leaking out.

The required mass of the bag would depend upon its specific strength, the pressure in the internal tunnels and the proportion of the asteroid hollowed out.  I used the thin walled pressure vessel equation to estimate the required thickness of the bag.  My assumption is that the bag is made from woven zylon fibres with an epoxy binder.  The break strength of zylon is 5.8GPa.  With the epoxy binder taking up 50% of volume, breaking strength would be reduced to about 3GPa.  For a 100m diameter bag, rated to a pressure of 50KPa, the minimum required thickness would be 0.42mm.  Applying a safety factor of 6 allows tolerance for micro meteorite damage and increases thickness to 2.5mm.  Assuming a density of 1250kg/m3 for a zylon-epoxy composite, total mass of the bag would be 98 tonnes.  This is light enough to be launched by near term heavy lift vehicles.

We could even spin the asteroid to generate internal gravity in the tunnels, although the bag would need to be stronger and heavier to accommodate this.  Natural light could be allowed to enter the interior, by cutting pits into the exterior of the asteroid, assuming that the bag can be made transparent.

If some 50% of the volume of the asteroid were excavated, then the asteroid would have enough internal space to house a thousand or so people, along with industries and manufacturing.


Interested in space science, engineering and technology.

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#2 2019-08-18 11:27:37

SpaceNut
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From: New Hampshire
Registered: 2004-07-22
Posts: 20,263

Re: Colonizing / terraforming small asteroids

Thank you for a good lead off to a topic Calliban, and welcome to NewMars.

We have lots of targets to which this could be done with but it still a lifting problem from earth to get critiacal mass of items that we need to achieve the building to ocupying steps.

Is there a favored target for teraforming?

Have we studied the possible resources that will be needed to support man?

What are the limits to the colony size?

Are there plans for this colony to be a deep space port to leverage from?

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#3 2019-08-18 13:13:15

Terraformer
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From: Lancashire
Registered: 2007-08-27
Posts: 3,340
Website

Re: Colonizing / terraforming small asteroids

Hmmm. I suspect it would make more sense to use the asteroid as a source of materials, and build a space habitat next to it. It's also been proposed to tunnel into asteroids and install large centrifuges, using the asteroid as radiation shielding. The trouble with spinning the entire rock is that they aren't likely to be strong enough to withstand it.

I *do* hope to see zero-g terrariums, though. Bags of gas around small rocks with trees growing through them, using for producing food and fibre.


"I guarantee you that at some point, everything's going to go south on you, and you're going to say, 'This is it, this is how I end.' Now you can either accept that, or you can get to work." - Mark Watney

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#4 2019-08-18 13:42:08

tahanson43206
Moderator
Registered: 2018-04-27
Posts: 4,148

Re: Colonizing / terraforming small asteroids

Hi Calliban,

You have introduced an interesting topic.

Calliban wrote:

I want to explore the idea of structurally reinforcing small asteroids with high strength polymers and carbon fibres to allow them to withstand internal pressure.  My base case is a 100m diameter asteroid.  If density is typical of a stony asteroid, it would mass 1.3 million tonnes.  Upon arriving at the asteroid, we would wrap it in a fibre reinforced polymer bag, with airlocks fitted into it.  The bag would then be tightened around the asteroid to provide prestressing.  We would them enter through airlocks and mine out the interior of the asteroid and pressurise the tunnels created.  The tunnels would probably have to be lined with a polyethylene wall paper to prevent air from leaking out.

I'd like to try to encourage you to focus on the idea you have presented.  It will be easy to be distracted, as more and more contributors pitch in to help you along.

As it happens, I have not run a search of the archive of the forum messages, to see if this topic has come up previously, but I would not be surprised if it had.

You might be able to find prior work in the forum archives that would help you along, or perhaps give you additional ideas, as Terraformer has done.

Please build on your initial post, whether or not other members join in.  Something you post may stimulate a member to add a thought, or perhaps a fact.

The protocol here allows you to defend your topic from inevitable side branches.

I am looking forward to seeing how far you can take this interesting topic.

(th)

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#6 2019-08-18 17:20:10

Calliban
Member
From: Northern England, UK
Registered: 2019-08-18
Posts: 603

Re: Colonizing / terraforming small asteroids

SpaceNut wrote:

Thank you for a good lead off to a topic Calliban, and welcome to NewMars.

We have lots of targets to which this could be done with but it still a lifting problem from earth to get critiacal mass of items that we need to achieve the building to ocupying steps.

Is there a favored target for teraforming?

Have we studied the possible resources that will be needed to support man?

What are the limits to the colony size?

Are there plans for this colony to be a deep space port to leverage from?

I raised the topic here precisely to explore these sorts of questions and to expose any flaws in the concept.

The purpose of wrapping the asteroid in a strong polymer bag is to allow mining to take place within a pressurised environment with at least some spin gravity (note: because of micro meteorite impacts, the bag itself would not remain airtight, but would provide a restraining force that allows tunnels in the asteroid to be pressurised).  The concept is analogous to a pre-stressed concrete pressure vessel, in which steel cables on the outside of a hollow concrete block provide a compressive force that balances the pressure inside.  As more material is excavated, more living space becomes available.  The asteroid evolves from a small outpost to a human colony and industrial centre incrementally, as living space expands and more equipment is delivered.

Whilst in the long-term, it would make more sense to construct purpose built habitats, as Terraformer suggests, the bag idea would appear to allow a group of colonists to arrive at an asteroid with a modest payload and rapidly convert it into a shirt-sleeve environment without the need to construct a large habitat using refined metals.  As soon as the bag is deployed, tunnelling machines would get to work excavating materials that would be processed and shipped back to near Earth space.  Human living areas would be set up in the empty tunnels left behind.  The practicality of the idea depends upon our ability to create the restraining bag using high specific strength materials.  In the initial example, a restraining bag weighing only 98 tonnes, allows access to an asteroid weighing 1.3million tonnes.  That is a ratio of 10,000:1.

In terms of resources, it would be ideal if we could find an asteroid with some inventory of water, carbon and nitrogen, as these are essential to life and it would be costly to ship these from Earth.  Given that the bag is functioning as a pressure vessel, its mass will be proportional to the volume enclosed, assuming that pressure stays the same.  Enclosing a 200m diameter body would require a bag weighing almost 800 tonnes, which is far beyond the lift capacity of near term heavy lift vehicles.  A 1km diameter asteroid would require a 98,000 tonne restraining bag, which is far beyond near term achievability.  On the other hand, enclosing a 50m diameter asteroid, would require a bag weighing just 12.25 tonnes.  This idea works best for small asteroids in the near term.

We would probably want to leave a layer of rock at least 2m thick between the bag and the tunnels closest to the surface.  This allows the a shell of rock to act as cosmic radiation shielding.  For very small bodies, this would waste a lot of material and there would be insufficient internal volume to be useful for habitats or equipment.  So I believe that near term practicality of the concept is for spheroid bodies some 30-100m in diameter.

I think the market for excavated material would be Earth itself for platinum groups metals and near Earth space for all other materials.  Bulk silicate might make useful reaction mass for transporting other more valuable materials to Earth orbit.  Transport will be via mass driver tugs.


Interested in space science, engineering and technology.

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#7 2019-08-18 17:41:15

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 20,263

Re: Colonizing / terraforming small asteroids

Depending on location several BFR once sent on the proper path would leave LEO with each a capability of a 100 passengers plus supplies or 100 tons of cargo given the manefest for what we want packed for the mission building of a teraformed small rock to planetoid.

The Bigelow Inflateables are multi layered to allow for micrometeor and possible radiation protection but nothing to this date has been manufacture for the scale of what you would consider.

I would look at modern day mining for how to make a safe controlled entrance that would be capped tight with crew to be sustained once a sizable cavern has been made but this means we would be a nuclear powered teraforming start. Assuming multiple air locks to the surface would be employed in order to keep air pressure conditions for man to work in free of space suits once the internal cavern is created.

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#8 2019-08-18 17:43:27

Calliban
Member
From: Northern England, UK
Registered: 2019-08-18
Posts: 603

Re: Colonizing / terraforming small asteroids

Thanks Spacenut.  Plenty to think about here and I will give the topics a read.

From what I have read elsewhere, the shell world concept involves using the gravity of the body to balance internal pressure, through the weight of a thick layer of rock balancing the pressure within.  In near Earth space, only a few of the largest asteroids have sufficient gravity to allow this at any atmospheric pressure useful to humans.  Eros is one; Ganymed another.  Phobos is probably massive enough.

ISRU fibreglass would allow us to bootstrap; starting with a small asteroid and building the fibreglass bag needed to hollow out a much larger one, perhaps a kilometre in diameter.  This would truly be large enough to house a million people if we hollowed it out, although disposing of waste heat would then be a problem.

In terms of location, it would be most productive to consider near term achievable targets.  That means near Earth objects with aphelion and perihelion not too far from 1AU; and as small as possible delta-V between the asteroid and low Earth orbit.


Interested in space science, engineering and technology.

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#9 2019-08-18 19:35:52

tahanson43206
Moderator
Registered: 2018-04-27
Posts: 4,148

Re: Colonizing / terraforming small asteroids

For Calliban re #8 (and prior) ...

There are members here who can help with physics, chemistry and (I'm pretty sure) mathematics, if you are willing to accept their input, and if your initiative interests them.

My interest is primarily in seeing this topic develop in a way which will help others later on.  The topic you have created would be a natural for a student to examine, if they are writing a paper or planning a project.  For this to work, (it seems to me), it will help for you to collapse uncertainty as soon as possible, in order to help the community to focus.

A good example is provided by Louis, who threw a mental dart at Mars, and came up with a location for Sagan City (2018).  With a firm location for Sagan City (2018), it is possible for others to build on that conceptual foundation.

In your case, I am hoping you will pick an asteroid you want to mine, and then stay with it until you have a shipment back on Earth to start collecting a return on the investment you will (by that time) have persuaded large numbers of people to support.

The details of the methods you will propose for this undertaking will shake out as you proceed.  Your initial proposal seems feasible as I read it, with the caveat that the final plan may look quite different from your starting vision.

In terms of location, it would be most productive to consider near term achievable targets.  That means near Earth objects with aphelion and perihelion not too far from 1AU; and as small as possible delta-V between the asteroid and low Earth orbit.

(th)

Last edited by tahanson43206 (2019-08-18 19:38:23)

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#10 2019-08-19 04:33:35

Calliban
Member
From: Northern England, UK
Registered: 2019-08-18
Posts: 603

Re: Colonizing / terraforming small asteroids

I have been looking at minor planet listings for suitable candidates, with diameter 30-100m and suitable orbital characteristics (aphelion and perihelion both ~1AU).  The most desirable candidates are in the Aten asteroid group.  Earth coorbitals would appear to require the least delta-V.  There are surprisingly few suitable candidates.
https://en.wikipedia.org/wiki/List_of_Aten_asteroids

Here are a couple, all at the lower end of the size range:
https://en.wikipedia.org/wiki/367943_Duende
https://en.wikipedia.org/wiki/2013_BS45

A 30m diameter restraining bag would weigh 2.6 tonnes.  Maybe all of the equipment needed can be launched to LEO with a single ITS launch.

This could be a stretch case at 160–360 meters:
https://en.wikipedia.org/wiki/(164207)_2004_GU9

One way of doing this would be to start with a bag capable of providing a 1KPa restraining pressure for an asteroid 360m in diameter and dig tunnels at a depth of say 100m and limit the density of tunnels to ensure that averaged pressure at the surface does not exceed 1KPa.  But that would mean digging an initial shaft 100m deep.  As the colony grew, additional restraining strips could be added to the surface, allowing the number of tunnels to increase.

Most of the candidates are too large for this scheme to be practicable.  For example, Bennu is a promising candidate in terms of composition and its orbit would appear to be workable.  But its diameter is almost 500m, requiring a restraining bag weighing about 10,000tonnes for a 50KPa restraining pressure or 2000 tonnes for a 10KPa restraining pressure and just 200 tonnes for 1KPa.
https://en.wikipedia.org/wiki/101955_Bennu

If Musk successfully develops the ITS launcher and meets his projected launch cost of $200/kg to LEO in reusable mode, then perhaps more ambitious projects are achievable.  A 4200 tonne restraining bag could be launched in LEO in 14 sections of 300te each.  When bolted together, these would provide a restraining bag sufficient for a 350m diameter asteroid.  If a mass driver tug could deliver them to the asteroid from LEO that is.

I begin to wonder, given that the market for any mined material is Earth or Earth orbit, if it would be more efficient to simply capture a small NEO and deliver it into Earth orbit using some of its material as reaction mass.  That way, processing equipment can be pooled in Earth orbit rather than shipping it out to numerous distant targets.  Not quite such an exciting idea, but possibly a more profitable one.  Asteroids in the size range of 30m in diameter, would mass about 30,000 tonnes.  We could use restraining bags to allow material to be mined from within them and then fed to mass drivers.

Could we shift that into high Earth orbit using mass driver engines within a few years?  How much power would we need say, if 1/3rd of the asteroid is used as reaction mass?  We are probably talking a delta-V of at least a 3km/s from an Aten asteroid to high Earth orbit.  Any thoughts?

Last edited by Calliban (2019-08-19 07:36:45)


Interested in space science, engineering and technology.

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#11 2019-08-19 07:28:17

tahanson43206
Moderator
Registered: 2018-04-27
Posts: 4,148

Re: Colonizing / terraforming small asteroids

For Caliban re #10 ...

Folks have been working this problem for a while, and there are books on the topic.  Would you be willing to share the list of books in your library, or which you have available for your research via online access?   Such a list would be helpful for anyone who might wish to offer a suggestion of another resource you might have missed.  SpaceNut (in particular but not exclusively) has demonstrated a (to my eye) remarkable ability to find online resources that pertain to topics members are building.

In addition, there is at least one corporation founded to mine asteroids, and there may well be others.  These would (presumably) have paid staff who are working the problem, and while much of their work will be kept in house, some may be revealed at conferences.

The direction you appear to be heading is of great interest to those who might wish to build an O'Neill colony in the Solar System, since materials are needed in great quantity for the larger designs.

Thanks for including links to online resources in your posts.  These should be helpful to students and practitioners alike.

(th)

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#12 2019-08-19 07:52:13

Calliban
Member
From: Northern England, UK
Registered: 2019-08-18
Posts: 603

Re: Colonizing / terraforming small asteroids

Hello tahanson,

Mining the Sky, by John Lewis and Case for Mars (Zubrin) are two of my favourite books.  Aside from that, I have various electronic resources and have access to Science Direct, through which I can access scientific publications.  There is a lot of general information on the internet now, which wasn't available 10-15 years ago.


Interested in space science, engineering and technology.

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#13 2019-08-19 08:47:17

tahanson43206
Moderator
Registered: 2018-04-27
Posts: 4,148

Re: Colonizing / terraforming small asteroids

For Calliban re #12 ...

Bravo!  The Lewis was the one I was thinking about, and agree that Zubrin is a great resource as well. 

Before I go much further here, I'd like to confirm that you are actually in a position to bring about changes in the real world (solar system in this case), and that you are psychologically prepared to make the sacrifices that would be required.  You can look at Musk and Bezos to see what top tier leadership looks like.

Most of us humans are content to support leaders.  My few attempts are leadership have not turned out well, but I keep trying.  In the mean time, I am occasionally rewarded for support of leaders at various levels.  A word of appreciation goes a long way in my book.  If you decide to try to become a Job Creator, I will try to provide whatever support I can, but you'll need to build a team.

There are people in the contributing membership who have confronted significant life challenges, and their advice and support may be available.

If you have not already done so, take a look at the writings of the moderators, who have earned a place in the forum structure.

There is way too much to read, so I'm suggesting you just skip about, trying to get a flavor of personalities and interests. 

Please note (if you decide to do this) that SpaceNut has been working to repair damage caused by a system crash several years ago, and you may run across damaged posts in need of attention.  If that happens you can let him know, so he can add the item to his (very long) list of tasks.


(th)

Last edited by tahanson43206 (2019-08-19 08:48:09)

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#14 2019-08-19 09:22:08

Calliban
Member
From: Northern England, UK
Registered: 2019-08-18
Posts: 603

Re: Colonizing / terraforming small asteroids

tahanson43206 wrote:

For Calliban re #12 ...

Bravo!  The Lewis was the one I was thinking about, and agree that Zubrin is a great resource as well. 

Before I go much further here, I'd like to confirm that you are actually in a position to bring about changes in the real world (solar system in this case), and that you are psychologically prepared to make the sacrifices that would be required.  You can look at Musk and Bezos to see what top tier leadership looks like.

(th)

Not sure what you mean.  I find the ideas interesting and would happily spend some time developing them.  But in terms of making this happen in the real world, that is the realm of governments and billionaires.  I'm not sure that I would want to make asteroid mining into a crusade that defines the rest of my life.  I am an engineer (mostly mechanical) and like to dabble with interesting concepts.


Interested in space science, engineering and technology.

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#15 2019-08-19 10:12:11

tahanson43206
Moderator
Registered: 2018-04-27
Posts: 4,148

Re: Colonizing / terraforming small asteroids

For Calliban re #14 ...

Thanks for your clarification, and for your decision to take a chance on the NewMars forum.

I hope you will find your scan of posts in the forum message database interesting and perhaps even occasionally inspiring.

It is possible that your interest in this topic, supplemented by input from existing members, might break trail for future trillionaires who would be researching how to mine or make habitats out of asteroids.  After all, we already have wealthy individuals pursuing that path. 

With the scope of your inquiry more defined, I am hoping you will engage with the community to defend your idea of enclosing an entire asteroid in a container. It is not clear to me why that is a good idea, but I am not the right person to evaluate it.

(th)

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#16 2019-08-19 18:38:03

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 20,263

Re: Colonizing / terraforming small asteroids

I think rather than trying to lift the bag we really need to be able to creat it insitu as the BFR or the ITS will require 6 ship tankers to get just the one beast loaded with payload out of orbit for the 100 ton that they could possibly do.

Then again using the insitu resources of the moon and lauching from there is a hugh boost in payloads to anywhere.,

I agree with the process to narrow down the possible targets for such an under taking that was in post #10


The bag approach is assuming that most are loose rubble at least on the outside and possibly not much better with void areas with in them.

The basalt fiber glass is also a insitu material to wrap the asteriod with in as it is desired to have a high tensile strength. Also as you bore into the core of it we could re-enforce its shaft entrance with more fiberglass as well. One we are deep enough to hollow it out once more line the would be floor with more fiber glass to seal the chamber before making an atmospher.

I would leave a false ceiling of the core with strut leggs to it so we can colorize it to project sunrise and sun sets as we spin the asteriod up for artificial gravity.

Just some thought keep or toss out...

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#17 2019-08-19 18:51:20

tahanson43206
Moderator
Registered: 2018-04-27
Posts: 4,148

Re: Colonizing / terraforming small asteroids

For SpaceNut re #16 ...

I'm hoping  Calliban will like your suggestions and expand upon them a bit ...

Thanks for clarifying why a bag would be useful.  For some reason I've had a concept of these objects as solid, but (of course) visiting probes have shown they can be loose collections of unfused material.

For Calliban ...

Our discussion of John Lewis inspired me to look at his Wikipedia record, and I was surprised to see how many books and other publications he has authored. Apparently, despite his age, he remains active in support of at least one corporation.

https://en.wikipedia.org/wiki/John_S._Lewis
Publications[edit]
    • Planets and Their Atmospheres: Origin and Evolution. 1984. ISBN .
    • Space Resources: Breaking the Bonds of Earth. 1987. ISBN .
    • Resources of Near-Earth Space. 1993. ISBN .
    • Physics and Chemistry of the Solar System. 1995. ISBN .
    • Rain of Iron and Ice: The Very Real Threat of Comet and Asteroid Bombardment. 1996. ISBN .
    • Mining the Sky: Untold Riches from the Asteroids, Comets, and Planets. 1997. ISBN .
    • Worlds Without End: The Exploration of Planets Known and Unknown. 1998. ISBN .
    • Comet and Asteroid Impact Hazards on a Populated Earth: Computer Modeling. 2000. ISBN .
    • Asteroid mining 101: wealth for a new space economy. 2014. ISBN .

I'm wondering about ordering Asteroid mining 101 .... It would be quite an update from the original.

(th)

Last edited by tahanson43206 (2019-08-19 18:53:08)

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#18 2019-08-20 08:47:39

tahanson43206
Moderator
Registered: 2018-04-27
Posts: 4,148

Re: Colonizing / terraforming small asteroids

For Calliban re topic ...

Would you be interested in working on setting up a radio beacon on Apothis?  The next pass of interest is in 2029, which should  be enough time to build a team and raise the funds for a mission.

https://en.wikipedia.org/wiki/99942_Apophis

Close approaches[edit]
The closest known approach of Apophis comes on April 13, 2029, when the asteroid comes to within a distance of around 31,000 kilometers from Earth's surface. The distance, a hair's breadth in astronomical terms, is ten times closer than the moon, and even closer than some man-made satellites.[23] It will be the closest asteroid of its size in recorded history. On that date, it will become as bright as magnitude 3.1[22] (visible to the naked eye from rural as well as darker suburban areas, visible with binoculars from most locations).[24] The close approach will be visible from Europe, Africa, and western Asia. During the approach, Earth will perturb Apophis from an Aten class orbit with a semi-major axis of 0.92 AU to an Apollo class orbit with a semi-major axis of 1.1 AU.

There are surely other strategies for planning, but I'd like to start discussion with a proposal to place a suitable vehicle in GEO, so that as the asteroid passes the vehicle can accelerate at sufficient rate to catch up and secure itself to the body.  The burn should be visible to the population, and there might be some funding opportunities with live video of the event, and a movie about the project.  The radio beacon would help planetary security teams to keep track of Apophis on its long trip out and back.

Louis ... is this your bailiwick?

(th)

Last edited by tahanson43206 (2019-08-20 08:53:51)

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#19 2019-08-20 17:15:46

Calliban
Member
From: Northern England, UK
Registered: 2019-08-18
Posts: 603

Re: Colonizing / terraforming small asteroids

Thanks chaps, some intriguing answers.  I will answer in more detail tomorrow; I have been away from my computer today.

Last edited by Calliban (2019-08-20 17:45:53)


Interested in space science, engineering and technology.

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#20 2019-08-20 20:40:08

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 20,263

Re: Colonizing / terraforming small asteroids

Since target locations are small the probes and satelites will be small to make use of the limited payload and lack of gravity. Rovers and tunnelers will also employ other technology to lock them to the surface for use. Such things as harpon anchors and climbing cables that wrap the little worlds so that it can stay put while it changes location. The anchor for boring a tunnel inward needs the means to allow it to cut inward while not distroying this little world of possible rubble. Think of this as tether to keep things put. The waste is collected from the boring and would be processed to form the filaments to make the fiberglass to wrap and seal the outside. Weave the filaments to form a blanket to wrap with. Use a UV cureable resin to make it work.

ISRU Polymers

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#21 2019-08-20 21:25:27

SpaceNut
Administrator
From: New Hampshire
Registered: 2004-07-22
Posts: 20,263

Re: Colonizing / terraforming small asteroids

I think that Robert Dyck has a Basalt topic but its evading me for the moment...3D printing at this post http://newmars.com/forums/viewtopic.php … 75#p127375

more composite 3D printing
https://www.fabbaloo.com/blog/2019/6/13 … salt-fiber

https://en.wikipedia.org/wiki/Basalt_fiber

https://basalt-fiber.com/

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#22 2019-08-21 05:30:25

Calliban
Member
From: Northern England, UK
Registered: 2019-08-18
Posts: 603

Re: Colonizing / terraforming small asteroids

SpaceNut wrote:

I think rather than trying to lift the bag we really need to be able to creat it insitu as the BFR or the ITS will require 6 ship tankers to get just the one beast loaded with payload out of orbit for the 100 ton that they could possibly do.

Then again using the insitu resources of the moon and lauching from there is a hugh boost in payloads to anywhere.,

I agree with the process to narrow down the possible targets for such an under taking that was in post #10


The bag approach is assuming that most are loose rubble at least on the outside and possibly not much better with void areas with in them.

The basalt fiber glass is also a insitu material to wrap the asteriod with in as it is desired to have a high tensile strength. Also as you bore into the core of it we could re-enforce its shaft entrance with more fiberglass as well. One we are deep enough to hollow it out once more line the would be floor with more fiber glass to seal the chamber before making an atmospher.

I would leave a false ceiling of the core with strut leggs to it so we can colorize it to project sunrise and sun sets as we spin the asteriod up for artificial gravity.

Just some thought keep or toss out...

Basalt fibre would appear to be an excellent ISRU material.  Reading some of the material that you have referenced, suggests that low iron basalt would be ideal (I believe stony asteroids are mostly olivine?) and melting point is typically 1500C.  We would need an electric furnace to melt the material and gravity to allow the melt to settle, allowing it to be drawn through dies.

Maybe the easiest solution in a limited space, would be to produce some woven, tensile strips and then filament wind the entire asteroid.  The tensile strength of basalt fibres is about 2GPa.  Using the thin walled pressure vessel equation, I estimate that some 16,000 tonnes of woven basalt fibre would be needed to enclose Apophis.

Spinning the asteroid does not appear to be practical.  If we were to spin it to produce 0.3g at its long ends, we would need longitudinal filaments capable of resisting the weight of the entire asteroid in an average gravity of 0.15g.  By my calculations, that implies a longitudinal force of 40GN, requiring some 140,000 tonnes of fibre for a 450m long asteroid, assuming a safety factor of 6.  That is almost an order of magnitude increase.  Maybe I have gone wrong somewhere.

Last edited by Calliban (2019-08-21 05:33:09)


Interested in space science, engineering and technology.

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#23 2019-08-21 06:37:20

tahanson43206
Moderator
Registered: 2018-04-27
Posts: 4,148

Re: Colonizing / terraforming small asteroids

For Calliban ...

Calliban wrote:

Basalt fibre would appear to be an excellent ISRU material.  Reading some of the material that you have referenced, suggests that low iron basalt would be ideal (I believe stony asteroids are mostly olivine?) and melting point is typically 1500C.  We would need an electric furnace to melt the material and gravity to allow the melt to settle, allowing it to be drawn through dies.

Thanks for picking up on the suggestion of designing for an encounter with Apothis in 2029!

The advantage of that choice (it seems to me) is that there will be likely to be global interest in the encounter, which should lead to funding opportunities at the level of nation states, and certainly selected corporations.

The quote above is interesting to me because I'm wondering if a centrifuge design for the melt process might work.  The patents for a working solution to this problem should be good for many years subsequently, because entrepreneurs will (most likely) be inspired to replicate the initial system throughout the solar system.

In case you have not had time to read the posts of other members, you will find that at least one member has secured a patent which is still in effect.

Your focus on mechanical engineering appears (to me at least) to be fortuitous for this situation.

As the first phase of securing a patent (as you probably know) it is necessary to perform a search, so it is possible patents already exist for centrifuge processing of melted metal.   Certainly centrifuge technology is well known and widely used for room temperature materials.  The circumstances of absence of gravity, presence of vacuum, and temperatures on the order of 1500C should provide opportunities for new patents, but prior work should be helpful for developing designs.

(th)

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#24 2019-08-21 16:56:34

Calliban
Member
From: Northern England, UK
Registered: 2019-08-18
Posts: 603

Re: Colonizing / terraforming small asteroids

Apophis' gravity is so weak (40 micro-g) that a rotating habitat massing a thousand tonnes on its surface would weigh only 40kg.  This could easily to tethered to the asteroid and supported by magnetic bearings.  The hab could contain both living space and a factory complex and would house a construction crew until they had manufactured and installed the restraining bag, at which point pressurised tunnels could be created.  The hab would immediately be sheltered from 50% of incoming cosmic rays by the bulk of the asteroid.

Spinning up the asteroid would take considerable time and would require a lot of reinforcement even to achieve lunar levels of gravity - some 4 times more than would be needed for pressure containment alone.  Building rotating habitats within voids dug out within the asteroid would appear to be a more cost effective choice.  However, some amount of gravity would assist mining and would allow excavated voids to be used as habitats without the need to create rotating habitats in void spaces, which would require motors and bearings and would generally be cumbersome.  The best solution would ultimately need to be arrived at by cost-benefit analysis.

I like the idea of Apophis as a colonisation target, as it comes close enough to the Earth that journey times to reach it in 2029, will be measured in hours.  Colonists will not have to endure months of space travel before reaching the target.  Those months can be spent setting up greenhouses, digging tunnels that take them away from space radiation and of course, manufacturing the restraining bag.  Given that Apophis regularly makes close approaches to Earth; returning home and returning mined minerals would appear to be much easier than it would be for other targets.

Last edited by Calliban (2019-08-21 17:29:17)


Interested in space science, engineering and technology.

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#25 2019-08-21 17:57:40

tahanson43206
Moderator
Registered: 2018-04-27
Posts: 4,148

Re: Colonizing / terraforming small asteroids

For Calliban re #24 and prior ...

A member of another space oriented group contacted me recently about another matter.  I described your interest in Apophis (noting your recent arrival here), and he replied with support for the idea of landing an instrument package on the asteroid in 2029.  This gent is from Canada.

Would your Prime Minister be interested in supporting an initiative to place instruments (for various purposes) on the asteroid in 2029?  I ask because with all the uncertainty immediately ahead for everyone in the British Isles, there may be some interest in striking a bold note for the future.

I can easily imagine multiple nation states and at least one major corporation having an interest in placing an instrument package on the asteroid in 2029.  This prospect increases in probability as commitments are made to undertake projects along these lines.

Your ambitious concept of building a habitat on (or in) the asteroid seems worth considering for future passes.  The first 7 year cycle would be sufficient time for the instrument packages to perform onsite sensing and to return the results to their sponsors.

Your concept (as I understand it) for a facility to attempt to make a kind of fabric out of the stony material of the body might be given a work out with a small experiment designed to analyze the material, and perhaps to attempt to melt it.

By any chance, do you know anyone with project management experience who might be willing to help design a plan for presentation to potential funders?

At this point, and for some time to come, this initiative would necessarily be carried out by volunteers.  As it happens, there are some significant talents "out there" in forum-land. 

Edit: As just one example of what may be possible if the initiative attracts people with the right skills, there is a need to plan a rocket which can wait in GEO until Apophis comes by, and then accelerate to match velocity.  The design of the vehicle itself, and computation of the orbital mechanics to achieve station keeping are significant challenges. 

Noting my lack of the required education and experience, I offer as a general observation that a solid rocket motor design might be better suited for this mission than a liquid fuel design.  The solid rocket motor (if chosen) could be supplemented with ion drive capability for fine tuning the approach to the body as it leaves the vicinity of Earth.

(th)

Last edited by tahanson43206 (2019-08-21 18:08:12)

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